Barrett's esophagus is a condition in which normal tissue in the lower esophagus is replaced by an abnormal, glandular tissue, which has a potential to undergo malignant transformation to cancer of the esophagus. Surveillance for malignant change is recommended, using regular upper gastrointestinal endoscopy. When malignant change becomes imminent, surgical resection is recommended. Recent evidence suggests that surgery might not always be necessary, as local ablative treatments may be sufficient. Photodynamic therapy sensitizes targeted tissues to light-activated chemistry, which has the potential to kill cells. Preliminary data suggest that premalignant changes of Barrett's esophagus may not progress to invasive cancer when treated with photodynamic therapy. This category D study randomizes patients with premalignant Barrett's esophagus to photodynamic therapy with regular surveillance, or to the more conventional treatment with medications designed to suppress acid formation in the stomach (omeprazole), with surveillance every three months. The surveillance includes upper gastrointestinal endoscopy and biopsy.